This application is a continuation of Application Ser. No. 198,385 filed on Oct. 20, 1980 and now abandoned.
This invention relates generally to a process for conducting solid state, free radical reactions.
More specifically, this invention relates to a process for generating and maintaining a concentration of free radicals on and in particles of a normally solid material by mechanical working of the material of cryogenic temperatures and thereafter carrying out a solid-solid reaction with another material.
It has been recognized, particularly in the Russian literature, that free radicals may be generated on macro-molecules at cryogenic temperatures by pulverizing polymer solutions in a vibrational mill. Subsequent reactions of the so-generated free radicals with certain low molecular weight substances were confirmed and studied by means of EPR techniques. An exemplary article setting out such investigations was authored by A. M. Dubinskaya and P. Yu. Butyagin, entitled, "Mechanical-Chemical Investigations of Some Free-Radical Reactions in the Solid Phase" and published in English translation in Kinetics & Catalysis, Vol. 9, pp. 839-846, July, 1968.
Typical of the approaches taken by these investigators was to dissolve a polymer in an appropriate solvent, place the solution in a sealed ampoule together with glass or steel spheres, freeze the solution by contacting the ampoule with liquid nitrogen and thereafter pulverize the frozen solution by vibrating the ampoule. Solid state, free radical reactions with solvent molecules and with reactive gases, principally oxygen, were confirmed and their reaction rates estimated. Experimentally derived reaction rate constants were found to be on the order of 10.sup.6 greater than was expected from extrapolation of literature data to low temperatures.
Those experimental techniques serve to confirm the development of free radicals on polymer molecules by mechanical activation at cryogenic temperatures and to confirm their reactivity toward certain low molecular weight compounds. However, the reaction technique disclosed by Dubinskaya, et al., is severely limited in that it is restricted to reactions between the free radical-containing polymers and certain reactive gases such as oxygen, and with certain low molecular weight liquids which also act as solvents for the polymeric material. Additionally, the technique disclosed by Dubinskaya, et al., is essentially impossible to scale-up to any practical production level.
There is disclosed and claimed in copending, commonly assigned patent application Ser. No. 117,235, a method for very rapidly dissolving polymeric materials in compatible liquids. The polymeric material is comminuted at cryogenic temperatures, as by hammer milling, and is thereafter mixed with a liquid preferably while still at cryogenic temperature. Dissolution of the polymer particles in appropriate liquids is extremely rapid; many orders of magnitude faster than is possible using conventional techniques. It is postulated in that patent application that the phenomenally increased dissolution rate obtained may be, at least in part, due to the presence of free radicals on and in the polymer particles created by the mechanical comminution. Dissolution activity of the polymer particles can be maintained for extended periods of time by storage at cryogenic temperatures, e.g., as a slurry in liquid nitrogen.